High strength gray cast irons



Jyw, w32., E B, COYLE 587,373

HIGH STRENGTH GRAY CAST IRONS Filed Jan. 5`. 1929 I ssheets-sheet 1 F. B. coYLE HIGH STRENGTH GRAY AsT IRoNs Filed Jan. 5, 1929 Ys sheets-sheet 2' b N Snom/6oz My E9, 11932 F. B, czoYL4 3,@675732 HIGH STRENGTH GRAY CAST IRONS.

Filed Jan. 5. 1929 SheeiS-Sheet 3 -a4 a aa UNITED STATES PATENT OFFICE FRANCIS B. COYLE, OF'JERSEY CITY, NEW JERSEY, ASSIGNOR NICKEL COMPANY, INC., A CORPORATION F DELAWARE HIGH STRENGTH GRAY CAST IRON S Application led January 5, 1929. Serial No. 330,534.

This invention relates to novel yhigh strength gray cast iron, of superior tensile strength which may be readily and economically machined, and to a method of producing this product.

It has heretofore been observed in connection with the production of gray cast iron that silicon and certain other materials function as precipitants lof carbon to drive it out of its combined into graphite form. Ithas also been observed that nickel could be employed in place of silicon as a precipitant of graphite. It was also noted that only a small increase in tensile strength was observed. In other' words, the conditions under which an appreciable increase in tensile strength could be cctained and the reasons underlying the change in properties were not discovered.

A somewhat similar method for the pro- 2 duction of gray iron castings was to employ calcium or magnesium silicide free from iron which was added supposedly for ridding the iron bath of occluded gases and to precipitate carbon in the iron. In this method the material might be added to molten white iron in the ladle or to the bath within the furnace and it was not determined what amounts of the material should be added or what proportions of ingredients were required in order to produce the desired product. It was recognized that the character of the gray iron produced might be varied by varying the proportion of the silicide added, but other eX- perimenters endeavoring to duplicate such results have failed to obtain a product of the character described, and consequently endeavors to obtain a product corresponding to that referred to in the prescribed manner have been wholly abandoned.

The present invention is based upon the discovery of a certain well deined relationship between certain elements in a mix adapted to produce high strength gray cast iron whereby a greatly increased tensile strength and certain other properties to be hereinafter more fully described might be obtained;

It was found that by maintaining certain es-y being drawn from the furnace or cupola and casting the material into molds within a suit-l able time interval to be determined in the manner hereinafter described from certain characteristics of the product that the desired results could be uniformly obtained under substantially all conditions in the treatment of material of the prescribed character.

One of the objects-of this invention is to provide amethod of treatment of cast iron mixes by which .increased tensile strength and other properties may be controlled so as to uniformly obtain a material of the desired properties.

.Another object of the invention is to provide a new product of the type described having constituents in ratios within certain proportions as hereinafter set forth.

A further object of this invention is the provision of an improved method of producing high 'strength gray cast irons by providing a mix` having relatively pure base materials in preponderating amounts and subsequently treating in a novel manner whereby to improve the homogeneityof the resulting product and to obtain enhanced physical strength.

Other objects and advantages will become more apparent as the detailed descriptionl below is read.

rlhe limitin ratios to obtain the desired results are in icated in the accompanying drawings in which:

Fig. 1 is a diagram which shows the maximum limit of strength of gray cast iron produced by conventional methods;

Fig. 2 is a similar diagram indicating the compositions susceptible of being benefited by -the improved process of the present invention; and Y fFig. 3` is a diagram showing the tensile strength of certain compositions hereinafter referred to.

The present invention comprehends the use of an improved' base material in order to substantially eliminate the necessity of adding 'ro THE INTERNATIONAL excessive amounts of scavenging agents remakes it possible to secure desired economies in production and subsequent forming operations by reason of the improved homogenelty of the resulting products.

As an example of a referred base material it has been found t at desirable results are secured by the use of a relatively cheap steel which may be readily secured in quantity and is characterized by the relative. freedom from sulphur, phosphorus and other deleterious substances.

This invention is preferably applied to a mix in the cupola containing over percent of steel and by adding thereto the necessary amount of graphitizer of the form hereinafter described, in the ladle after the melted charge has been passed thereto, or while the melted charge is passing to theladle. In addition to a charge including 60 percent or more of steel, which is preferably employed, there \is added a balance of return scrap, and/or pig iron, and/or alloys such as ferrosilicon and nickel alloys, and sufficient coke of a satisfactory variety, which should ordinarily be added in excess of the usual ratio. The ratio which is employed in the charge is preferably about eight or less of the steel to one of coke. These charges are preferably first preheated in the cupola without turning on the blast by burning coke at the bottom thereof. This preliminar operation serves to heat up the charge and t e cupola lining in order that the resulting iron may issue from the furnace in a reasonably hot condition. With the charge is also added preferably enough ferro-silicon or other suitable siliconbearing material .in amounts adequate to introduce from .7 5 to 1.25 percent silicon in the metal as tapped from the cupola. The blast is then turned on until the charge is completely melted in the usual manner and the char e is then tapped out and is graphitized in t e ladle. The foregoing description relates in the main to cupola melting, but it is to be understood that the melting may be carried out successfully in other types of furnaces.

The graphitizer which is |preferably employed in theV melted mixcomprises either aluminum, silicon or nickel, or mixturesof any two or three of these elements, which, as stated, must be added to the melted charge while being drawn olf or after it has been drawn oif into a ladle, in order that the time element for precipitating carbon in the desired graphitic form may be adequately controlled in accordance with the test hereinafter referred to. The amount of graphitizer to be added may be determined in each case from knowledge of the composition of the charge by referring to Fig. 2 herein to bring the amounts or ratios of carbon to graphitizer within the enclosed areas of the charts as will be described more in detail.

It is to be understood that addition of other materials besides graphitizer may be made in the ladle either in con] unction with the graphitizer or separate therefrom. Furthermore, the graphit'izer may be added in the form of a pure metal or in the form of a ferro alloy although it is preferred to add materials which will dissolve in the melt without introducing foreign elements or slag-producing materials. For example, it is preferred to avoid the use of calcium and magnesium silicide as they introduce slag-forming or foreign materials into the melt.

The reasons for the advantages resulting from the addition of the graphitizer in proportions to produce ratios of carbon to graphitizer within the operative areas in Fig. 2 hereof and permitting the operation of the graphitizer for a limited period of timeis not completely understood although by following the instructions herein, the desired results may be uniformly obtained. It appears probable, however, that since a large proportion of the carbon present is in the form of iron carbide, there are substantially no graphite nuclei present, and on the addition of a graphitizer, suchas silicon and/or nickel, and/or aluminum after the melt has left the furnace and before it is poured into molds, the graphitizer has a limited period for precipitating the graphite. Thus, the graphite nuclei do not have sufficient time to grow to any substantial extent before the metal sets, and, hence, does not develop tothe same extentas would take place by adding the graphitizer charge in the cupola beforethe melt or portion thereof is withdrawn. According to this theory, the uncombined carbon in the gray cast iron does not have a sufficient period of crystal growth to produce relatively large graphite flakes, and this apparently is the reason for the improved result obtained by the addition of the graphitizer in the ladle after the charge has been withdrawn from the .furnace or cupola. It seems tobe apparent, therefore,

that if the graphitizer were added in the furnace or cupola, the gra hite nuclei would have a longer time for evelopment or for crystal growth into graphite flakes. The amount of time necessary for the formation of graphite flakes in the molten metal in the ladle obviously varies with operating conditions butin the ordinary case the molten metal in the ladle should be poured within about 20 to 35 minutes after the addition of the graphitizer. In any given case, however, the correct time of pouring may be readily determined by the use of a test sample which may be separately cooled and tested in the usual manner.

Referring more particularly to Fig. 1, the ordinates represent the total percentage of carbon while the total percentage of the silicon is indicated by the abscissae in the figure. The solid lines AB, AC, AD, and AE repreizo and pearlite.

ent being sent a diagram published by Maurer (Kruppsche Monatschefte July, 1924). AThe compositions represented in the areas enclosed between the coordinate axes and the various lines indicate the structure of the irons when produced under normal conditions of foundry practice. That is, if the carbon and silicon are present in the proportions enclosed by the area ABO, lwhen the metal is cast under normal conditions, its structure will consist essentially of excess combined carbon and austenite, or transition products from austenite to pearlite. More o'r less graphite will also be present, but free iron carbide will be present in excess of the eutectoid proportion.

Referring again to Fig. 1 of the drawings, proportions of carbon and silicon present in amounts corresponding to that represented within the area ABC will produce a structure which will consist essentially of' graphite and pearlite with patches of iron carbide. The proportions of silicon andcarbon represented by the area. enclosed by AGD will produce a structure consisting of graphlte The structure of castiron containing carbon and silicon in the proportions corresponding'to that represented within the area ADE will consist of graphite with pearlite and ferrite, the amount of pearlitefpresgreater than the amount of f errite. Proportions of carbon and silicon represented by the area tothe right of the line AE will produce a structure consisting of Graphite, ferrite and pearlite, the amount o f ferrite being greater than that of pearlite.

In Fig. l the superimposed broken line areas represent compositions or ratios of carbon and silicon which will give certain ranges of tensile strength. In other words, these broken line areas represent the correlation of tensile strength with carbon and silicon content. TheseA areas have been determined from a large number of tests of various gray cast iron compositions. With carbon and silicon present in the ing to that included within the area ALO,

the tensile strength is less than 30,000 pounds per square inch. With carbon and silicon in the proportions represented within the area ALM exclusive of the areas VXYZ and PQRS, the tensile strength is 30,000 to 35,000

pounds per square inch. jWith carbon and silicon in the proportions included in the area WXYZ, exclusive of the area PQRS, the tensile strength is from 35,000 to 40,000 pounds per square inch. With carbon and silicon in the proportions included in the area PQRS, the tensile strength is found to be from about 40,000 to 45,000 pounds per square inch. With carbon and silicon in the proportions included in the area AMN the tensile strength of the product is less than v30,000 pounds per square inch.

Reference is made to Fig. 2 of the accomproportions correspond-v and silicon whicliathe base melt should contain in ort-,der that'the process be successful. It has been found that the addition of graphitizers (that is, elements which favor the precipitation as graphite of carbon from solution, or aid in the decomposition of iron carbide with an accompanying precipitation of graphite) will, if added to such a base melt in the ladle, or after taking this White or mottled iron out of the furnace, appreciably increase the tensile strength and im'- prove the product. It is preferred, in carrying out the present inventions, to add any of nickel, silicon, or aluminum, either singly or mixed, or in combination with each other or other elements, to obtain this desired increase-in tensile strength. For example, in a molten cast iron,produced according to this invention, containing carbon and silicon in the proportion included "in the above designated area F, G, H, I, of Fig. 2, if silicon be added in the ladle in such quantity that the yfinal composition will contain carbon and silicon inthe proportions included within the area J, K, L, M of Fig. 2, castings made from such a molten iron will possess a 'structure and will possess a tensile strength substantially 10 percent or more higher as shown by Fig 3, than that of the same composition when prepared and. cast in accordance with ordinary foundry practice.

If another graphitizer were' used, the diagram would retain the same'form, but the points B, C, D, and E wouldlpbe located at different percentages of graphitizer contained. However, the vertical limits of the areas FGI- II and J KLM would remain the same, butthe lines GI-I, JM, and KL would stand in the same relationship to the lines AB, AC, and ADin their new position as is represented in Fig. 2 for the position of the lines AB, AC and AD When nickel alone is used as a graphitizer, the quantity thereof will usually bel about twice as much as the silicon employed for the same purpose. However, the maximum amount would be about 5.5 percent.

Referring now to specific examples, I will compare three examples of my process with the same iron when untreated in the ladle. In this case, in treatment A, eight ounces of aluminum per hundred pounds of molten iron and ten ounces of ferro-manganese 7 0% Mn) per hundred pounds of molten iron were added to the ladle. The ferro-manganese addition, generally, has no specific effect as a graphitizer, and is employed primarily as a deoxidizing hundred pounds of molten iron there were added twenty-four ounces of ferro-silicon set forth therein.V

agent. In treatment `B, to each Si) and ten ounces of ferro-manganese Mn). v

In treatment C, to each hundred pounds of molten iron, there were added twelve ounces of ferro-manganese (70% Mn), eight ounces of ferro-silicon (50% Si) and twenty-four ounces of ferro-nickel shot (95% Ni). A

The following table gives a comparison in each of these three cases of the treated material and the untreated material:

Total carbon.. 284 2.75 2.75 2.97 2.64 2.44 Manganese 21 47 21 45 24 74 46200 55690 41180 61320 290 302 163 Treatment N one. A N one. B None C If other graphitizers are used or mixtures thereof, they may be evaluated in terms of the equivalent amount of silicon and the equivalent amount of such graphitizer, either alone or in combination with silicon used in accordance with the silicon chart. For example, two parts of nickel would roughly equal one part of silicon, and one part of aluminum would roughly equal one and onefourth parts of silicon. These are merely illustrative examples. I prefer to use silicon and nickel either alone or together as a graphitizer, either with or without other additions.

Referring now to Fig. 3, there is shown a constitutional diagram representing the alloys comprehended in this invention, in which both nickel and silicon are employed in combination with the improved base material to produce an improved series of high strength gray cast irons. of the improved compositions are indicated generally by curves showing the specific ratios of the silicon and nickel contents. It will be readily observed that curve I divides the area included in the diagram so as to distinguish those compositions giving a tensile strength of less than 50,000 lbs. per sq. inch from those rhaving a strength greater than gr 50,000 lbs. per sq. in. Curve II shows the minimum limits of those compositions having tensile strengths of4 more than 60,000 lbs.

per square inch.

When the tensile strengths are referred 4to herein it will be understood that they are substantially always determined by results de-j rived from the standard test bars which are sometimes known as arbitration bars.

The ranges of tensile strength p limits of the ratios of nickel and silicon for tenslle strengths of 50,000 lbs. r sq. in. The area included between curve and point 6 of the diagram shows the ratios of nickel and silicon in high strength cast ironsy in which the tensile strength isv greater than 50,000 lbs. per sq. in.` Within this area covered by curve I and the point 6, it is possible to indicate the ratios of nickel and silicon which give tensile strengths of 60,000 pounds per sq. in. and over; such indication is shown by curve II. Such ratios are ineluded within the area 6, 7, 8, 9, 10, and 1l...

It will be seen, therefore, that the compositions having from 50,000 to 60,000 lbs. per sq.- in. tensile strength will fall within the are comprehended between curve I and point 6, minus the area formed by curve II and point 6. Likewise it will be seen the alloys of greater than 60,000 poundsper square inch are-found in the area of curve II, and

point 6. j4

For purposes of reference it may be indicated t at curves I and II preferably correspond to the ratios of nickel and silicon, as indicated below: i

Curve I 'rom Ni Reference point I Ni Si and Si Per rent l 5. 0 1. 625 6. 625 2, 3. o 1. 2 4. 2 'i 1. 5 1. 2 2. 7 4 1. 1 2. 4 3. 5 5 .-.1...- 1.6 4.0 5.6

Curve II While the foregoing description in respect to the curves I and II refer to the preferred ay cast irons of strengths greater than 50,000 lbs. per sq. in., and by reason of which these irons have high commercial value, it will be understood, that gray cast irons between 40,000 and 50,000 lbs.l per sq. in. are advantageous and are high strength -irons when compared to the Inormal gray cast irons.

In respect to these high strength cast irons between 40,000 and 50,000 lbs. per sq. in., there is illustrated curves III and IV which,

lao

Curve III Total N1 Reference point N1 S1 and S1 Per cent 12 5. 0 30 5. 3 1'! 4. 0 31 4. 31 14 2. 5 42 2. 92 15 1. 25 62 1. 87 16 0 1. 05 1. 05

Curve IV Per cent l. 15 l 4. 0 v 15 70 3.60 4. 30 55 3. 4 3. 95 20 3. 0 3. 20 0 2. 7 2. 70

vproifed and efficient high strength gray cast irons may be readily and economically produced by the process of the present invention,

by adding to the base composition previously considered, percentages of nickel and silicon I as defined and set forth in the accompanying diagram (Fig. 3) the compositions required to give any desired tensile strength being readily chosen by those skilled in the art without the necessity of making experimental melts or any substantial number of laboratory tests.

For purposes of more fully setting forth the advantages of the invention it may be stated Vthat high strength gray irons with no nickel ingredient showed an increase in tensile strength with various adjusted compositions. It was thereafter learned from eX- periments that there was a noticed improvementin the tensile strengths When nickel was added. With varying'amounts of nickel the irons showed various strengths but in each instance the tensile strength was higher than could be obtained without nickel. The method herein is obviously applicable to higher compositions of nickel and even may run as high as 50 percent nickel if desired.

It may be Inoted that other methods may be employed to produce these advantageous high strength gray cast irons 'so long as nickel is included. Also it has been found that when i I s It has also been found that the addition of nickel gives a substantial improvement in the tensile strengths of heavy castings, and it is well known that heavy castings made of ordinary gray iron which have the required strengths are difficult to cast. It has therefore been determined by reason of experiments that various percentages of nickel are of particular value in producing diiiicult castings of relatively large sections. Also it has been found that the lighter or small castings, as well as the heavy and diliicult castings, are found to be sound and dense and have greater strength throughout and particularly in the center of such sections when nickel is added.

The advantages of this invention will readily be apparent to those skilled in the art since a highly economical, cheap, simple, and

effective method is provided by which a series seA of gray cast irons may be synthetically produced to form an improved material. The resulting cast irons have superior tensile strengths and uniformity of composition, and at the same time, are sufficiently soft as to be readily and economicallymachined Without having to resort to the necessity of grinding.

The specific graphitizer'used may be varied as above indicated, so long as the saine is in metallic form, although the ones above mentioned are preferred, alone or in combination, and with or Without other additions. The

cast irons may contain metallic alloy ingrel dients, if desired, and other changes may be made in the practice of this disclosure without departing from the spirit and scopel of this invention. f

This application is a continuing application in part of my co-pending application, Serial Number 191,035, filed May 13th, 1927.

What is claimed is:

1. The process of making machinable, gray cast iron having a tensile strength above 50,000 pounds per square inch which comprises melting a charge containing at least 60% of steel scrap and the balance ferrous metals or alloys, which when solidified by cooling in the usual manner against anonchilling surface would yield l'non-machinable,

weak, White or mottled iron, tapping such,

molten, white or mottled iron into a. ladle, transforming said Weak, White or mottled iron to gray ironl by adding to said molten White or mottled iron nickel and silicon to an extent of more than about 2.5% and less than about 7.0%, the nickel constituting more than about 1% and less than about 5%, permitting the thus-treated molten metal to stand for a limited' period of time only sufficient to cause the distribution of carbon in the form of thoroughly distributed fine particles of graphite and insufficient for the formation and growth of large graphite Hakes, controlling the aforesaid period to less than about 20 to 35 minutes, and before the expiration f content of about 2.5% to aboutV 3.1%, nickel of the vsaid controlled, restricted period of time, pouring the thus-treated molten metal into conventional, non-heated and non-chillv ing molds whereby a machinable gray cast iron comprising a ne pearlitic and sorbitic ground mass containing fine particles of nodular, dendritic graphite distributed throughout said ground mass and having a tensile strength in excess'of 50,000 pounds per square inch and.J containing a low carbon content f about 255% w about 3.1%,nicke1 more than about 1.00% and less than about 5.00% and silicon` more than about 1.00% and-less than about 4.00%.

2. The process of making machinable, ray cast iron. having a tensile strength a ove 50,000 pounds per square inch in a cupola which comprises melting a charge containing at least 60% of steel scrap, about 12% of coke, about 1 part of coke being used to 8 parts or less of steel, and the balance ferrous metals or alloys, which when solidified by cooling in the usual manner against a nonchilling surface would yield non-maohinable, weak, white or mottled iron, tapping such molten white or mottled iron into a ladle, transforming said weak, white or mottled iron to gray iron by adding to said molten white or mottled iron nickel and silicon to an extend of more than about 2.5% and less than about 7.0% ,the nickel constituting more than about 1% and less than about 5%,

permitting the thus treated /molten metal to stand for a limited period of time only suiiicient to cause the distribution of carbon in the form of thoroughly distributedneparticles of nodular, dendritic graphite and insuicient for the formation and growth of large graphite flakes, controlling the aforesaid period to less than about 20 to 35 minutes,

Aand before the expiration of the said lcontrolled, restricted period of time, pouring the thus treated molten metal into conventional non-heated yand non-chilling molds whereby a machinable ,gray cast iron comprising a fine pearlitic and-sorbitic ground mass conyC-ainin dendritic graphite and having a tensile strength in excess of 50,000 pounds per square inch and containing a low carbon more than about 1.00% and less than about 5.00% and silicon more that less than about 4.00%.

I FRANCIS BrCOYLE.

finely-divided particles of nodular, Y

about 1.00% and l 

